Photolithographic process for producing etched patterns on the surface of fine tubes, wires, or other three dimensional structures

ABSTRACT

The present invention involves a photolithographic process, and apparatus and material for use therein, for producing etched or eroded areas or holes in a selected pattern on or in the surface of fine workpieces, such as small diameter tubes. One aspect of the present invention is a photolithographic process for producing a selected pattern on a nonplanar surface of a workpiece using at least one mask to define the selected pattern. The process includes the acts of applying a photoresist material to the workpiece and aligning the mask with the nonplanar surface of the workpiece. The mask may have an inner surface that corresponds to the nonplanar surface. The process may also include the acts of exposing and developing the photoresist material.

TECHNICAL FIELD

[0001] The present invention generally relates to photolithography. Moreparticularly, it involves a photolithographic process, and apparatus andmaterial for use therein, for producing etched or eroded areas or holesin a selected pattern on or in the surface of fine workpieces, such assmall diameter tubes.

BACKGROUND

[0002] Many applications, particularly in the biomedical field, requirea flexible, three dimensional member. Stents, for example, are commonlyused in angioplasty procedures for the treatment of coronary arterydisease. The afflicted artery is dilated/expanded in these proceduresthrough the use of an angioplasty balloon. Without artificialreinforcement, however, the balloon-expanded vessel has a tendency toconstrict to its previous obstructed internal diameter shortly after theangioplasty procedure. By implanting a stent along the expanded portionof the vessel, the vessel is provided with sufficient radialreinforcement to prevent the vessel from constricting.

[0003] A variety of conventional techniques exist for manufacturingstents. One such technique involves forming wire members about acylindrical support member, such as a mandrel, so as to overlap orintertwine with one another. The wire members are joined together at theintersection points using conventional bonding techniques, such aswelding, blazing or soldering. Once the wire members are suitablyinterconnected, the mandrel is removed from the wire members, therebyleaving an elongated wire mesh tube having a plurality of openingsdefined between the individual wire members. Another conventionalmanufacturing technique is to cut a pattern of openings into athin-walled stainless steel tube using electro-mechanical or lasermachining techniques.

[0004] One problem with these conventional techniques, however, is thatthey are expensive and time consuming. This problem is compoundedbecause very little cost savings can be achieved by making a largequantity of stents. In addition, stents made by conventional techniques,particularly the techniques using mechanical and electro-mechanicalprocesses, have practical size limitations due to the number of holes orbonds (frequently>4000) required to make the leading 5-6 inches of thestent sufficiently flexible.

[0005] One possible solution to these problems is photolithography.Conventional photolithographic techniques are desirable because amanufacturer can use a single mask in conjunction with well-knownetching processes to inexpensively produce a large number of stents.Photolithography is also desirable because marginal production costs aresubstantially independent of the complexity of the desired pattern. Thatis, although a large number of openings will increase the cost of makingthe mask, the number of openings will not greatly affect the costsdirectly associated with making an additional stent.

[0006] One problem with conventional “state of the art”photolithographic techniques, however, is that they use a flat mask.This flat mask cannot project a useful image onto the three dimensionaland/or nonplanar structures used in medical devices without makingcomplex and expensive changes to the mask pattern. Another problem withconventional “state of the art” photolithography is that the maskpatterns are generally fabricated by sputtering metal or other opaquematerials onto a smooth glass plate. These plates, however, are fragileand are susceptible to scratching.

[0007] Clearly, there is a need for a simple, inexpensive, and robustmethod and apparatus that can produce a usable photoresist pattern forthree-dimensional process requirements. In particular, there is a needto produce usable patterns of photoresist on the surface of relativelyfine cylinders, (i.e., 10-15 mil OD tubes or wires) with the objectiveof permitting the etching by chemical or plasma techniques of a desiredtexture (wires) or holes (tubes).

SUMMARY

[0008] The present invention provides a photolithographic process forproducing etched patterns on the surface of fine tubes, wires, or otherthree dimensional structures. In particular, the present inventionproduces usable three-dimensional photoresist patterns on the surface offine cylinders. This photoresist pattern can permit chemical or plasmaetching of a desired texture on wires or of desired holes in tubes. Oneembodiment of the present invention comprises the following apparatusand material: a cleaning agent, a photoresist agent or solution, a mask,a developer solution and a resist remover. An appropriate exposing lightsource is provided. Each of the preceding may be selected or matchedwith the composition and configuration of the workpiece and with thesolutions or chemicals. The selected mask and/or mask holder may bemachined to carry or exhibit a selected pattern of slots or exposureopenings, and may include one or more alignment notches, pins or thelike. The present invention is well-suited for use on fine cylindricalor tubular workpieces, in which case a curved mask is used. For tubularworkpieces, the interior or lumen thereof may be protected from beingplugged or occluded by removably lodging a plug therein or by filling itwith a suitable removable material.

[0009] The present invention also provides a photolithographic method ofproviding a workpiece with an etched area comprising applying a suitablephotoresist material to the workpiece, providing a mask with a desiredpattern corresponding to the etched area, aligning the mask and theworkpiece, and exposing and developing the photoresist material. Moreparticularly, the process or method of the present invention comprisesproviding a subject workpiece, applying a suitable photoresist solutionto the workpiece, providing a mask with a desired pattern, aligning themask and the workpiece, exposing the resist, treating the exposed resistin a developer solution, etching the workpiece in an appropriate manner,and removing the resist. Appropriate intervening and complimentary stepsmay be included in the process of the present invention. For example,the workpiece may be cleaned and dried prior to the application of thephotoresist solution, the resist coated workpiece may be baked orotherwise cured, and the workpiece may be rinsed and/or dried afterimmersion in the developing solution and/or after the application of theresist remover. These steps may involve chemical solutions or agentstailored to the workpiece material, and/or to the selected photoresist,developing and resist removal solutions. The conditions of and in whichthe process takes place may be optimized for specific applications orworkpieces.

[0010] Some embodiments of the present invention include aphotolithographic process for producing a selected pattern on anonplanar surface of a workpiece using at least one mask to define theselected pattern. The process comprises the acts of applying aphotoresist material to the workpiece and of aligning the mask with anonplanar surface of the workpiece. The mask in these embodiments maycorrespond to the nonplanar surface.

[0011] The present invention also includes a photolithography apparatusfor forming an offset pattern in a tubular workpiece and aphotolithographic method of forming a radially spaced offset pattern ona three dimensional workpiece. The photolithography apparatus in someembodiments comprises a stage having a hemicylindrical substrate channeladapted to receive a tubular workpiece, a hemicylindrical mask definingat least one aperture, a first stop associated with the stage andadapted to position the workpiece in a first position relative to themask, a second stop associated with the stage and adapted to positionthe workpiece in a second position relative to the mask, and an exposinglight source adapted to illuminate the tubular workpiece through the atleast one aperture. The photolithographic method in some embodimentscomprises the acts of placing a workpiece on a stage, jogging theworkpiece against a first stop, exposing a first portion of thephoto-sensitive coating through a mask, rotating the workpiece, joggingthe workpiece against a second stop, and exposing a second portion ofthe photo-sensitive coating though the mask. The workpiece in thismethod has a photo-sensitive coating.

[0012] An advantage of the present invention is that it may be used toproduce a selected pattern of holes on or in a workpiece having a smallcross-sectional area or diameter more cost efficiently than machining.Another advantage of the process of the present invention is that it iswell suited for producing a selected pattern of a large number of offsetholes on or in a fine cylindrical or tubular workpiece. For example, itmay be used to render a workpiece or portion thereof more flexible byproviding for the partial or complete erosion of the surface of theworkpiece in a pattern comprising a plurality of opposed, offset erodedareas about the circumference of the workpiece for a selected lengththereof.

[0013] These and other features and advantages of the present inventionwill become more fully apparent and understood with reference to theenclosed descriptive material and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1A is a perspective view of a workpiece having a slot patternproduced by the present invention.

[0015] FIGS. 1B-1D are, respectively, a top plan view, an end view, anda front view of the workpiece in FIG. 1A.

[0016]FIG. 2 is a flow chart illustrating one method of making theworkpiece in FIGS. 1A-1D.

[0017]FIG. 3A is a perspective view of one three dimensional maskembodiment.

[0018] FIGS. 3B-3D are top plan, sectional, and side detail views of afirst rectangular slot pattern embodiment for the three-dimensional maskof FIG. 3A.

[0019] FIGS. 3E-3G are top plan, sectional, and side detail views of anoval slot pattern embodiment for th& three-dimensional mask of FIG. 3A.

[0020] FIGS. 3H-3J are top plan, sectional, and side detail views of asecond rectangular slot pattern embodiment for the three-dimensionalmask of FIG. 3A.

[0021]FIGS. 4 and 5 are sectional views depicting the relationshipbetween arc-length and precision of one embodiment of the presentinvention.

[0022]FIG. 6 is a sectional view of one selected workpiece having awire/plug and a photoresist coating.

[0023]FIG. 7A is a top plan view of one mask holding fixture embodimenthaving a mask embodiment attached thereto.

[0024]FIG. 7B is a fragmentary top plan view of the mask holding fixtureembodiment of FIG. 7A, with the mask removed for clarity.

[0025]FIG. 7C is a detailed plan view of the mask alignment pins inFIGS. 7A and 7B.

[0026]FIG. 8A is a perspective view of the mask holding fixture of FIGS.7A-7C with an attached base.

[0027]FIG. 8B is a perspective view of the mask holding fixture of FIG.8A, with the mask removed for clarity.

[0028]FIG. 8C is a detailed perspective view of the mask alignment pinsin FIGS. 8A and 8B.

[0029]FIG. 9A is a sectional view of one selected workpiece having aplug wire and a photoresist coating.

[0030]FIG. 9B is a sectional view of the embodiment in FIG. 9A showingthe wire plug bent 90° across the workpiece.

[0031]FIG. 9C is an end view of the embodiment shown in FIG. 9B.

[0032]FIG. 10 is a tube angular indicator.

[0033]FIG. 11 is a sectional view of one mask, mask holding fixture, andworkpiece with an indicator pointer positioned at 0 degrees.

DETAILED DESCRIPTION

[0034] The present invention depicts a process and an apparatus that maybe adapted to create various patterns or shapes in or on a workpiece,including eroded areas of various depths, sizes and shapes. The specificapplication discussed in this disclosure is providing a pattern for theetching of holes in a NiTi tube (such as Nitinol) to enhance theflexibility of a portion of its length. However, the techniques areequally applicable to producing a texture on a solid workpiece. Thoseskilled in the art will realize that other applications of these methodsand apparatus are also within the scope of the present invention.

[0035] The basic solution for this specific application is in thedevelopment of a technique where the photomask is a machinedhemicylinder (i.e., a half-cylinder) of slightly larger inner diameter(“ID”) than the outer diameter (“OD”) of the objective pattern receiver,with holes machined in the hemicylindrical mask in a positive image ofthe desired pattern. The conformity of the mask with the objectiveallows the production of the desired pattern on the curved surface ofthe objective wire or tube. The pattern formed on a portion of thetarget can be stepped around the target by incremental rotation of thetarget. This invention also includes a process for coating a finecylindrical surface with a layer of photoresist, for producing ageometrically compliant pattern mask, and for using a rotate/jogtechnique to form a complex pattern on the surface of said cylinderusing a relatively simple mask.

[0036] FIGS. 1A-1D depict a tubular workpiece 12 having an exteriorsurface 13, a cylindrically shaped interior lumen 14, and a slot pattern18. In this embodiment, the slot pattern 18 consists of a plurality ofgenerally rectangular holes 20 having a width of about two mils and alength of about eight mils. The holes 20 are arranged so that opposite(i.e., 180 degrees apart) holes are directly across from each other andso that adjacent (i.e., 90 degrees apart) holes are staggered by about2-3 mil. The pattern 18 in this embodiment is formed in the first 5-6inches of a 5 foot long, 17 mil OD, 10 mil ID Nitinol tube. Theobjective of the pattern 18 is to render the 5-6 inch length of tube 12far more flexible and softer than the original tube 12. Those skilled inthe art will recognize that other workpiece materials and patterns 18are within the scope of the present invention.

[0037] The tubular workpiece 12 in this embodiment has a pair ofU-shaped alignment notches 15 ground into one end 24 of the tube 12. Aswill be described in more detail with reference to FIGS. 9-11, thisalignment notch 15 can be used to help position the tube 12 while usinga step/jog technique. Dimension A, the distance between a tip 28 of thenotch 15 and a top 30 of the notch 15, is arbitrary. However, dimensionA in embodiments using the step/jog technique should be greater thandimension C, the pattern the offset distance. Dimension B, the distancebetween the tip 28 and the pair of holes 20 closest to the tip 28,should equal the sum of dimensions A and C.

[0038]FIG. 2 is a flow chart depicting one method of forming the pattern18 in the workpiece 12. At step 100, a manufacturer forms a mask 42having a surface that corresponds to the nonplanar surface of theworkpiece. FIG. 3A is a perspective view of a hemicylindrical mask 42suitable for use with a cylindrical workpiece 12. This mask 42embodiment has a hemicylindrical outer surface 44, a hemicylindricalinner surface 46, and a pair of planar clamping surfaces 48. The portionof the mask 42 located between the outer surface 44 and the innersurface 46 defines a plurality of mask apertures 50 arranged into a maskpattern 52. FIGS. 3B-3J are top plan, sectional, and side detail viewsof three different mask aperture 50 embodiments suitable for thethree-dimensional mask 42 in FIG. 3A. Specifically, FIGS. 3B-3D and3H-3J depict two different rectangular aperture embodiments, while FIGS.3E-3G show an oval aperture embodiment. Those skilled in the art willrecognize that the mask patterns 52 depicted in FIGS. 3A-3J may extendfor the entire desired length for the pattern or for a portion thereof.

[0039] The mask 42 may be made from any material that is compatible withthe chosen machining technique and that has relatively good dimensionalstability. The chosen material should also be sufficiently wearresistant so that the mask 42 can be used to produce patterns 18 onlarge number of workpieces 12. Suitable materials include, without beinglimited to, stainless steel, aluminum, brass, and bronze. Polymeric,glass, ceramic masks 42 are also within the scope of the presentinvention. It is desirable to fabricate the mask 42 such that thediameter of the curved inner surface 46 is slightly larger than the sumof the OD of the workpiece tube 12 and the photoresist layer 36thickness.

[0040] Referring again to FIG. 2, a desired pattern 52 is formed in anappropriately shaped mask blank at step 102. In some embodiments, thedesired pattern 52 is machined into the blank using a precision,computer-controlled machining technique, such as electrical dischargemachining (“EDM”), hydrodynamic machining, or laser-beam machining. Itis highly desirable, nearly to the point of being imperative, that themachining and/or deburring process used to fabricate the mask 42 providea smooth burr free finish to prevent scratching of the photoresist layer36.

[0041] Those skilled in the art will recognize that the dimensions ofthe pattern 52 are determined by the degree of columniation of theexposure light source (not shown), by the desired dimensions of theholes 20 to be formed in the workpiece 12, and by the radial position ofthe holes. That is, as shown in FIGS. 4 and 5, the thickness of thephotoresist layer 36 will allow some light beams 55 to pass between themask 42 and the workpiece 12. These light beams will illuminate an arc,labeled “D” in FIG. 4 and “E” in FIG. 5, below a top edge 49 of the maskaperture 50. The length of this arc will depend on the angular width andlocation of the mask aperture 50. Apertures 50 having a top edge 49located closer to the 90-degree point will produce a shorter arc thanwill those located farther away (i.e., arc E<arc D).

[0042] At step 104 in FIG. 2, a particulate and contamination freeexterior surface 13 is prepared for photoresist adhesion. Those skilledin the art will recognize that the selection of a cleaning agent and acleaning methodology is guided by material compatibility with theworkpiece 12 in use and by the contaminants requiring removal. Someembodiments of the present invention use an acidic, neutral, or alkalinedetergent system coupled with the use of ultrasonic agitation. Thischoice is driven by the workpiece material and the level of organiccontaminants on the exterior surface 13. After cleaning, the part 12 isrinsed thoroughly with deionized water (“DLH20”) and dried thoroughlyinside and out.

[0043] Embodiments having interior lumens 14 should be sealed at step106 so that the lumen 14 does not become clogged with photoresist. Onesuitable method of sealing the lumen 14 is to insert a plug 32 into thelumen 14. FIG. 6 shows a plug 32 embodiment suitable for use in acylindrical lumen 14. The plug 32 in this embodiment is a cylindricalwire having an OD slightly smaller than the ID of the lumen 14 and alength somewhat greater than the workpiece 12. The wire can be made fromany material. However, it is desirable that the wire be made from amaterial that is relatively unaffected by the chemicals and processingenvironments used to pattern the workpiece 12. For example, a steelworkpiece 12 could use a stainless steel wire. Similarly, a Nitinolworkpiece 12 could use a platinum (“Pt”) wire because it would be inertto the usual etchant (i.e., HF/HNO3), thus reducing the possibility ofhydrogen embrittlement known to be a concern within NiTi tubes. Otherplug 32 embodiments capable of releasibly sealing the lumen 14 are alsowithin the scope of the present invention.

[0044] Next, at step 108, the workpiece 12 is coated with photoresistand baked. In order to provide a photoresist layer 36 of appropriatethickness to withstand the physical contact of mask alignment and thechosen etching environment, the workpiece 12 can be dip coated in asuitable liquid photoresist, such as SHIPLEY PHOTOPOSIT SP 2029-1manufactured by the Shipley Company, Inc. This particular photoresist isdesirable because its solids content (i.e., its viscosity) may bealtered to produce a coating 36 of about 6-10 micrometers thick when theworkpiece is withdrawn at about 5-10 cm/in. However, any light sensitivechemical capable of bonding to the workpiece 12 and capable ofwithstanding the chosen etching environment is within the scope of thepresent invention.

[0045] The coating 36 can baked onto the workpiece 12 in any appropriatemanner, such as 30-45 minutes at 80-90 degrees Celsius in a forced draft(preferred) or in a convection oven. Those skilled in the art willrecognize that the above specific conditions referenced can vary andshould be optimized for differing applications.

[0046] Embodiments using a dip process for applying the photoresist willgenerally have a small “bulb” 38 of photoresist at the end of the plug32. This bulb 38 may be snipped off or left intact as determined by anyinterference caused in the subsequent align and expose steps. If snippedoff, it is desirable to leave as much of the plug 32 protruding aspossible.

[0047] At step 110, the mask 42 is aligned with the workpiece 12. FIGS.7A-7C and 8A-8C show a stage 56 embodiment that may be used toaccurately position the workpiece 12 relative to the mask 42. This stage56 embodiment has a hemicylindrical substrate channel 58 machined intoits top surface 60, a pair of mask alignment pins 66, and a vacuum port68. The substrate channel 58 has a first stop 62 and a second stop 64located near one end. A mask holding fixture 70 fits over the mask 42and holds it against a perforated area 71 of the top surface 60. Thestage 56 may, in turn, be connected to a hollow base 72. The hollow basedefines a vacuum manifold 74 that operably connects the vacuum port 68to a vacuum source (not shown).

[0048] The mask 42 and the workpiece 12 may be aligned in thisembodiment by placing the photoresist-coated workpiece 12 in thehemicylindrical channel 58 and by pushing the workpiece 12 against oneof the stops 62 or 64. The mask holding fixture 70 is then closed overthe workpiece 12, the alignment is checked, and a vacuum is pulledbetween the stage 56 and the mask holder 70 to provide an intimatecontact between the workpiece 12 and mask 42.

[0049] Referring again to FIG. 2, a UV exposure lamp (not shown) isfired at step 112 to expose those portions of the photoresist layer 36that are not protected by the mask 42. At step 114, the exposed resist36 is immersed in a suitable developer solution, such as SHIPLEYPHOTOPOSIT 303A (an aqueous alkaline developer). At step 116, theexposed resist 36 is dissolved away using an appropriate solvent.Completion of this step 116 leaves a positive image of the slot pattern18 in the photoresist coating 36. The part is then thoroughly rinsed inDLH20 and blown dry.

[0050] After developing and rinsing, the part is inspected to assure thequality and integrity of the generated pattern. FIG. 6 depicts an area76 requiring special inspection attention for damage to the photoresist36. At step 118 in FIG. 2, those portions of the workpiece 12 exposedduring step 116 are controllably eroded away using a suitable etchingprocess. Suitable etching processes include, without being limited to,chemical, plasma, and reactive ion etching.

[0051] After the etching step 118 is complete, the plug wire 32 isremoved and workpiece 12 is immersed in an appropriate photoresistremover, such as SHIPLEY PHOTOPOSIT REMOVER 112A. The workpiece 12 isthen thoroughly rinsed and washed with appropriate solvents, such asacetone followed by isopropyl alcohol. Those skilled in the art willrecognize that steps 104-118 can be repeated on another workpiece 12using the same mask 42.

[0052] FIGS. 9-11 illustrate a step/jog technique that may be used tocreate a complex pattern 18 using a comparatively simple mask 42.Specifically, FIGS. 9A-9C show a portion 34 of the plug wire 32 thatprotrudes 2-3 cm beyond the end of the workpiece 12. This protrusion 34may be bent into an approximate 90-degree angle and used to relate theangular position relationship between the mask 42 and the workpiece 12.Embodiments using this “indicator pointer” 35 should have a sufficientfrictional fit between the plug wire 32 and the cylindrical lumen 14 ofthe tube 12 to preclude spontaneous or unintended relative motion. Thatis, there should be enough friction so that the wire 32 will not rotaterelative to the tube 12 unless the manufacturer intends for suchrotation. The length of the bent indicator pointer 35 is arbitrary.However, those skilled in the art will recognize a precise angularposition can be observed more easily with a longer indicator pointer 35than with a shorter indicator pointer 35.

[0053] The indicator pointer 35, or another device capable of indicatingrelative angular position, can be used to repeat the mask pattern 52 atregular intervals around the circumference of the workpiece 12. Thefirst step in one such embodiment is to align the indicator pointer 35at 0 degrees (see FIG. 10) with the workpiece 12 jogged against thefirst stop 62. The UV exposure lamp is then fired to expose thoseportions of the photoresist layer 36 that are not protected by the mask42. Next, the indicator 35 is aligned at 90 degrees with the workpiece12 jogged against second stop 64. The UV exposure lamp is fired a secondtime to expose the mask pattern 52 onto a second portion of thephotoresist layer 36. Those skilled in the art will recognize that thefirst stop 62 sits inside the notch 15 and does not contact theworkpiece 12 when the workpiece 12 is jogged against the second stop 64(see FIG. 11). The next step is to expose the photoresist layer a thirdtime with the indicator 35 at 180 degrees and with the workpiece 12jogged against the first stop 62. Finally, the workpiece is aligned andexposed with the indicator 35 at 270 degrees and with the workpiecejogged against the second stop. Those skilled in the art will recognizethat a similar procedure could be used to generate a different radialspacing and/or pattern offsets and that the basic manufacturing processcould be easily automated using well-known manufacturing techniques.

[0054] The present invention provides numerous advantages overconventional manufacturing techniques. For example, the presentinvention provides a method of using a nonplanar mask to produce largenumbers of small holes or slots on a nonplanar workpiece. The presentinvention also provides a method of using a machined metal mask toaccurately generate photolithographic patterns on three dimensionalworkpieces. In addition, the present invention uses the techniques of“rotating” and “jogging” of the workpiece to produce relativelycomplicated patterns with a comparatively simple mask. This rotating andjogging technique can, in particular, be used to fabricate a radiallyspaced, offset pattern on the circumference of a tubular workpiece.

[0055] Although the present invention has been described in detail withreference to certain embodiments thereof, variations are possible. Forexample, the methods and apparatus described in this specification couldbe used on non-cylindrical workpieces 12. Those skilled in the art willrecognize that the mask 42 and the stage 56 in these embodiments couldbe altered to receive the nonplanar surface(s) of that particularworkpiece 12. In addition, the present invention could use multipleoffset light sources, rather than a single overhead light source toreduce the “thickness” effect described with reference to FIGS. 4 and 5.The present invention could also use a stepping motor or othercontrollable actuating apparatus, in place of or in conjunction with thestops 62 and 64, to align the workpiece 12 with the mask 42. Also, themask 42 in some embodiments could be made from a flexible or compliantmaterial and could be laid over the nonplanar surface of the workpiece12.

[0056] Those skilled in the art will also recognize that theaccompanying figures and this description depicted and describedembodiments of the present invention, and features and componentsthereof. With regard to means for fastening, mounting, attaching orconnecting the components of the present invention to form the mechanismas a whole, unless specifically described otherwise, such means wereintended to encompass conventional fasteners such as machine screws, nutand bolt connectors, machine threaded connectors, snap rings, screwclamps, rivets, nuts and bolts, toggles, pins and the like. Componentsmay also be connected by welding, friction fitting, adhesives, ordeformation, if appropriate. Electrical connections or position sensingcomponents may be made using appropriate electrical components andconnection methods, including conventional components and connectors.Unless specifically otherwise disclosed or taught, materials for makingcomponents of the present invention were selected from appropriatematerials, such as metal, metallic alloys, fibers, polymers and thelike, and appropriate manufacturing or production methods includingcasting, extruding, molding and machining may be used. In addition, anyreferences to front and back, right and left, top and bottom and upperand lower were intended for convenience of description, not to limit thepresent invention or its components to any one positional or spacialorientation. Therefore, it is desired that the embodiments describedherein be considered in all respects as illustrative, not restrictive,and that reference be made to the appended claims for determining thescope of the invention.

We claim:
 1. A photolithographic process for producing a selectedpattern on a nonplanar surface of a workpiece using at least one mask todefine the selected pattern, comprising: a) applying a photoresistmaterial to the workpiece; and b) aligning the mask and the nonplanarsurface of the workpiece.
 2. The method of claim 1, wherein the mask hasa first surface that corresponds to the nonplanar surface.
 3. The methodof claim 1, further comprising: exposing and developing the photoresistmaterial.
 4. The method of claim 1, further comprising: cleaning thenonplanar surface with a detergent; and rinsing the nonplanar surfacewith deionized water.
 5. The method of claim 1, further comprising:baking the workpiece and the photoresist material in an oven.
 6. Themethod of claim 1, wherein the act of developing the photoresistmaterial comprises: immersing the photoresist material in a developersolution.
 7. The method of claim 1, further comprising: developing theexposed photoresist material to uncover a portion of the workpiece; andetching the exposed portion of the workpiece.
 8. The method of claim 7,wherein the act of etching the exposed portion of the workpiececomprises: immersing the workpiece in a chemical etchant.
 9. The methodof claim 7, wherein the act of etching the exposed portion of theworkpiece comprises: placing the workpiece in a plasma.
 10. The methodof claim 1, wherein the workpiece is metallic.
 11. The method of claim1, wherein the workpiece is nitinol.
 12. The method of claim 1, whereinthe workpiece is cylindrical.
 13. The method of claim 1, wherein theworkpiece defines an interior lumen.
 14. The method of claim 13, furthercomprising: plugging the interior lumen with a plug.
 15. The method ofclaim 14, wherein the plug comprises platinum.
 16. The method of claim14, wherein the plug comprises stainless steel.
 17. The method of claim14, wherein the interior lumen is cylindrical and wherein the plug is awire.
 18. The method of claim 1, further comprising: exposing a firstportion of the photoresist material; rotating the workpiece relative tothe mask; and exposing a second portion of the photoresist material. 19.The method of claim 18, further comprising: providing a radial alignmentindicator; and using the radial alignment indicator to radially positionthe workpiece.
 20. The method of claim 19, wherein the radial alignmentindicator serves as a plug to minimize the intrusion of processchemicals into an interior opening of the workpiece.
 21. The method ofclaim 1, further comprising: providing a fixture adapted to allowobservation of the relative radial location of the workpiece and themask.
 22. The method of claim 21, wherein the workpiece is a cylindricaland wherein the mask is a hemicylinder.
 23. The method of claim 1,wherein the mask comprises a material chosen from the group consistingof stainless steel, aluminum, brass, and bronze.
 24. The method of claim1, wherein the mask defines a plurality of apertures.
 25. The method ofclaim 24, wherein the apertures are substantially rectangular.
 26. Themethod of claim 24, wherein the apertures are substantially oval inshape.
 27. The method of claim 24, wherein a first portion of theapertures are substantially rectangular and wherein a second portion ofthe apertures are substantially oval in shape.
 28. The method of claim1, wherein the mask has a smooth interior surface.
 29. The method ofclaim 1, further comprising: providing a first stop and a second stopjogging the workpiece against the first stop; rotating the workpiece;and jogging the workpiece against the second stop.
 30. The method ofclaim 29, further comprising: machining an alignment notch into theworkpiece, the alignment notch adapted to receive the first stop. 31.The method of claim 1, wherein the selected pattern comprises aplurality of opposed, offset areas.
 32. A method of forming a selectedpattern on a nonplanar surface, comprising: a) providing a workpiecehaving a nonplanar surface; b) cleaning the workpiece; c) applying aphotoresist layer over the nonplanar surface; d) providing a mask thatcorresponds to the nonplanar surface, the mask defining an aperture; e)aligning the mask over the nonplanar surface; f) shining a light throughthe aperture, thereby exposing a first portion of the photoresist layer;g) rotating the workpiece relative to the mask; h) shining the lightthrough the aperture, thereby exposing a second portion of thephotoresist layer; i) removing the first portion and the second portionof the photoresist layer from the workpiece; and j) placing theworkpiece in an etchant.
 33. The method of claim 32, further comprising:repeating the acts of rotating the workpiece relative to the mask andshining the light through the aperture, thereby exposing at least oneadditional portion of the photoresist layer.
 34. An photolithographyapparatus for producing a selected pattern on a nonplanar surface of aworkpiece, comprising: a stage having a receiving area adapted toreceive the workpiece; and a mask having an inner surface adapted toreceive the nonplanar surface, the mask defining at least one aperture.35. The apparatus of claim 34, further comprising: a stop associatedwith the stage and adapted to align the workpiece with the mask.
 36. Theapparatus of claim 35, further comprising: an exposing light sourceadapted to illuminate the workpiece through the at least one aperture.37. An photolithography apparatus for forming an offset pattern in atubular workpiece, comprising: a stage having a hemicylindricalsubstrate channel adapted to receive a tubular workpiece; and ahemicylindrical mask defining at least one aperture.
 38. The apparatusof claim 37, further comprising: a first stop associated with the stageand adapted to position the workpiece in a first position relative tothe mask; and a second stop associated with the stage and adapted toposition the workpiece in a second position relative to the mask. 39.The apparatus of claim 38, further comprising: an exposing light sourceadapted to illuminate the tubular workpiece through the at least oneaperture.
 40. A photolithographic method of forming a radially spacedoffset pattern on a three dimensional workpiece, comprising: a) placinga workpiece on a stage, the workpiece having a photo-sensitive coating;b) jogging the workpiece against a first stop; c) exposing a firstportion of the photo-sensitive coating through a mask; d) rotating theworkpiece; e) jogging the workpiece against a second stop; and f)exposing a second portion of the photo-sensitive coating though themask.
 41. The photolithographic method of claim 40, further comprising:repeating the acts of rotating and jogging to obtain a circumferentialpattern around the workpiece.